Bicycle MechanicsBroken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Upon examination of the headset, the mechanic noticed a cracked steerer tube just above the crown. The suggestion was first a warning that the bike should not be ridden and that a replacement should be installed. The fork blades itself and the dropouts and the crown are ok. So is the head tube and bearings.

First, what is the likely cause of this type of fracture. Its maybe less than an inch above the crown and is less than half the circumfrence of the steerer tube.

The bike is near 2 years old with about 7,500 miles of riding. This summer going downhill for about 2 miles, the bike started to shimmy, wobble uncontrollably at speeds of maybe 35-40 mph. By braking I got it to slow down but still managed to eject head first over the bars as I came to a near stop speed. Initially, that wobble felt more like a rear flat but the frame shook uncontrollably in short time.

Second, does this type of fracture occur frequently? Is it due to riding or what?

Count yourself very lucky that the steerer didn't separate completely before you stopped riding the bike.

No, this is not a common or frequent failure and most forks can be used for decades. It was either a material defect or the result of a severe impact at one time. BTW, what are the fork and steerer materials?

I had a steer tube on an old French bike bend on me. The steering started binding and I could see that the headset cups were coming out of the frame. I liked that bike but it wasn't worth the price to change the fork to one of modern dimensions.

Count yourself very lucky that the steerer didn't separate completely before you stopped riding the bike.

No, this is not a common or frequent failure and most forks can be used for decades. It was either a material defect or the result of a severe impact at one time. BTW, what are the fork and steerer materials?

The bike is a 2005 model and the fork is carbon. The steerer tube outer shell is a carbon like material and the inner part is metal according to the mechanic.

Two year old bike with a steerer failure. Sounds like a warranty issue to me. Take it to the shop you bought it from or contact the manufacturer if that's not an option. If, however, you damaged the steerer when you crashed then you're going to be buying a fork.